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Abstract:

A bow wave in a composite laminate generated during part consolidation is
reduced by transmitting atmospheric pressure loads to a region of the
part having low compaction pressure due to bridging of a vacuum bag at an
edge of the part.

Claims:

1. A method of reducing a bow wave in a composite laminate part during
consolidation, comprising: transmitting atmospheric pressure loads to a
region of the part having low compaction pressure due to bridging of a
vacuum bag at an edge of the part.

2. The method of claim 1, wherein the region of low pressure is located
at an edge of a radius in the part, and transmitting atmospheric pressure
loads includes applying the transmitted pressure loads at the edge of the
radius.

3. The method of claim 1, wherein transmitting atmospheric pressure loads
includes placing a caul on the part at the region of low compaction
pressure.

4. A method of reducing a bow wave produced in a region of low compaction
pressure of a first uncured composite part during consolidation in a
vacuum bag with a second composite part, comprising: placing a caul
device over the first and second parts covering the low pressure region;
and using the caul device to apply atmospheric pressure loads to the low
pressure region of the first part.

5. The method of claim 4, wherein the low pressure region is along an
edge of a radius on the first part, and placing the caul device includes:
placing a first caul over the radius and the edge of the radius on the
first part, and placing a second caul on the second part overlapping the
first caul.

6. The method of claim 4, wherein using the caul device to apply
atmospheric pressure loads includes using the second caul to apply
pressure to the first caul in the low pressure region.

7. A method of compressing a radius section of a fiber reinforced
laminate part during consolidation, comprising: forming a large radius in
the part adjacent the radius section; and applying compaction pressure to
the part, including applying tension on the fibers in the radius section
by compressing the fibers in the large radius.

8. The method of claim 7, wherein forming the large radius in the part
includes forming an excess curved flange on the part.

9. The method of claim 7, wherein applying the compaction pressure
includes: placing a vacuum bag over the part, placing the vacuum bagged
part in an autoclave, drawing a vacuum in the bag, and applying pressure
to the bag using the autoclave.

10. A device for reducing a bow wave at an edge of a radius on a
composite laminate part during consolidation, comprising: a caul
configured to substantially conform to the shape of the radius and apply
compaction pressure to the part at the edge of the radius.

11. The device of claim 10, wherein the caul includes: a first portion
adapted to be placed on, and apply pressure to the radius, and a second
portion having an extremity overlying the first portion and the edge of
the radius.

12. The device of claim 11, wherein the first and second portions of the
caul are formed integral with each other.

13. Apparatus for tensioning fibers in a radius of a fiber reinforced
composite laminate part during consolidation comprising: a mandrel having
a large radius in an excess flange area of the mandrel.

14. The apparatus of claim 13, wherein the large radius has a radius
greater than that of the radius of the part.

15. A device for reducing a bow wave generated at an edge of a radius of
a composite laminate part during consolidation, comprising: a caul for
applying pressure to the radius of the part, the caul including a first
portion adapted to cover the radius and the radius edge, and second
portion overlying the first portion and the radius edge for applying
pressure to the radius edge through the second portion of the caul.

16. The device of claim 15, wherein the first portion of the caul is
tapered in thickness around the radius.

17. The device of claim 15, wherein the second portion of the caul
overlies the first portion of the caul and the radius edge.

18. The device of claim 15, wherein the first and second portions of the
caul are integral with each other.

19. A device for reducing a bow wave generated along an edge of a radius
of a composite laminate spar being joined to a stiffener having lower
flanges adjacent the radius edge during consolidation, comprising: a
first curved caul for applying pressure to the radius edge and having a
thickness that is tapered along its curvature; and a second caul formed
integral with the first caul, the second having laterally extending
flanges respectively overlying the lower flanges of the stiffener and
having an extremity overlying the radius edge for transmitting
consolidation pressure from the flanges of the stiffener to the radius
edge through the first caul, the second caul further including a web
adapted to be sleeved over the stiffener.

20. A method of fabricating a composite structure assembly including a
laminate spar joined to a stiffener, comprising: forming and precuring
the stiffener; laying up the laminate spar on a mandrel having a radius;
assembling the precured stiffener with the spar, including placing a
layer of adhesive between a lower flange of the stiffer and a web of the
spar; installing a caul device on the assembly, including molding a first
portion of the caul device to an end of the stiffener overlying a lower
flange on the stiffener, and molding a second portion of the caul device
integral with the first portion, including molding the second portion to
conform to a radius formed in the spar; vacuum bagging the assembly;
placing the assembly in an autoclave; and using autoclave pressure to
consolidate the assembly, including using the caul device to transmit
pressure from the lower flange to an edge of the radius formed in the
spar.

Description:

TECHNICAL FIELD

[0001] This disclosure generally relates to methods and equipment for
fabricating fiber reinforced resin laminates, and deals more particularly
with a method and device for compressing a radius in the laminate.

BACKGROUND

[0002] Fiber reinforced resin laminates may be consolidated prior to
and/or during curing in order to eliminate voids and other
inconsistencies in the cured part. Consolidation may be achieved by
applying pressure to the uncured laminate using vacuum bagging and/or
autoclaving processes. In some cases, a caul plate is placed between the
vacuum bag and certain areas of the laminate such as a radius, in order
to assure that the applied pressure is evenly distributed over these
areas. In some part geometries, regions of low pressure may exist over
the part for any of a variety of reasons, such as bridging of the vacuum
bag over certain features of the part. These low pressure areas may
result in a "bow wave" being generated in the outer plies of the
laminate, in which an out-of-plane wave of the plies is forced from
regions of high pressure to the regions of the low pressure mentioned
above. Bow waves are undesirable because they result in out-of-plane
fiber distortions that may cause voids in the laminate.

[0003] Accordingly, there is a need for a method and a device for reducing
bow waves in fiber reinforced resin laminates during consolidation,
particularly those that may occur near the edge of a radius in the
laminate. There is also a need for reducing regions areas of low pressure
on the laminate caused by bridging of a vacuum bag.

SUMMARY

[0004] The disclosed method and device reduce bow waves in the laminate
plies caused by bridging of a vacuum bag used to consolidate the
laminate. The device is relatively simple in construction, is reusable
and easily installed. The device is used to compress a region of low
pressure area on the laminate, such as an edge of a radius, caused by
bridging of the bag over the radius edge. The device includes a first
caul covering the radius, and a second caul covering the first portion
and the radius edge. The second caul may also overlie a second laminate
such that consolidation pressure applied to the second laminate is
transferred through the second caul onto the radius edge. In one
embodiment, the first and second cauls may be integrated to form a single
unit. In other embodiments, multiple devices may be joined together
side-by-side. The disclosed embodiments may reduce bow waves in laminates
during the consolidation process, resulting in cured parts which may
exhibit reduced voids and inconsistencies, and desired mechanical
properties.

[0005] According to one disclosed embodiment, a method is provided of
reducing a bow wave in a composite laminate part during consolidation.
The method comprises transmitting atmospheric pressure loads to a region
of the part having a low compaction pressure due to bridging of a vacuum
bag at an edge of the part. The region of low pressure may be located at
an edge of a radius in the part. Transmitting atmospheric pressure loads
may include applying the transmitted loads at the radius edge using a
caul on the part at the region of low pressure.

[0006] According to another embodiment, a method is provided of reducing a
bow wave produced in a region of low compaction pressure of a first
uncured composite part during consolidation in a vacuum bag with a second
composite part. The method comprises placing a caul device over the first
and second parts covering the low pressure region, and using the caul to
apply atmospheric pressure loads to the low pressure region of the first
part. The region of low pressure may be along an edge of a radius on the
first part. Placing the caul includes placing a first caul over the
radius and the radius edge on the first part, and placing a second caul
on the second part overlapping the first caul. Using the caul to apply
pressure includes using the second caul to apply pressure to the first
caul in the region of low pressure.

[0007] According to a further embodiment, a method is provided of
compressing a radius section of a fiber reinforced laminate part during
consolidation. The method comprises forming a large radius in the part
adjacent the radius section, and applying compaction pressure to the
part, including applying tension on the fibers in the radius section by
compressing the fibers in the large radius. Forming the large radius in
the part includes forming an excess curved flange on the part.

[0008] According to still another embodiment, a device is provided for
reducing a bow wave at an edge of a composite laminate part during
consolidation. The device comprises a caul configured to substantially
conform to the shape of and apply compaction pressure to the edge. The
edge may be located along a radius in the part, and the caul includes a
first portion adapted to be placed on and apply pressure to the radius,
and a second portion having an extremity overlying the first portion and
the edge of the part. The first and second portions of the caul may be
formed integral with each other.

[0009] In still another embodiment, apparatus is provided for tensioning
fibers in a radius of a fiber reinforced composite laminate part during
consolidation. The apparatus comprises a mandrel having a large radius in
an excess flange area of the mandrel, wherein the large radius has a
radius of curvature greater than that of the radius of the part.

[0010] In another embodiment, a device is provided for reducing a bow wave
generated in a radius of a composite laminate part during consolidation.
The device comprises a caul for applying pressure to the radius of the
part. The caul includes a first portion adapted to cover the radius and
an edge contiguous to the radius in which a bow wave in the part is
generated. The caul further includes a second portion overlying the first
portion and the edge of the part for applying pressure to the edge of the
part through the second portion of the caul.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

[0011] FIG. 1 is an illustration of a side view of a composite structure
assembly.

[0012]FIG. 2 is an illustration of a side view taken in the direction `2`
in FIG. 1.

[0013]FIG. 3 is an illustration of an enlarged sectional view showing the
formation of a bow wave in the upper plies of the spar at the end of the
stiffener.

[0014]FIG. 4 is an illustration of a sectional view of the composite
structure assembly, showing the use of a caul device to reduce the bow
wave shown in FIG. 3.

[0015] FIG. 5 is an illustration of a sectional view of a first caul
forming part of the caul device shown in FIG. 4.

[0016]FIG. 6 is an illustration of an end view of a second caul forming
part of the device shown in FIG. 4.

[0017]FIG. 7 is an illustration of a perspective view of the second caul.

[0018] FIG. 8 is an illustration of a perspective view of one side of the
stiffener shown in FIGS. 1-4 having the second caul installed thereon.

[0019] FIG. 9 is an illustration of an isometric view of another form of
the caul device being installed on the stiffener.

[0020] FIG. 10 is an illustration of a perspective view of one side of
another embodiment of the caul device.

[0021]FIG. 11 is an illustration of an isometric view of the opposite
side of the caul device shown in FIG. 10.

[0022] FIG. 12 is an illustration of the caul device shown in FIGS. 10 and
11 installed on a pair of the stiffeners.

[0023] FIG. 13 is an illustration of a sectional view of a laminate
assembly showing an alternate method of reducing bow waves.

[0024]FIG. 14 is a simplified flow diagram illustrating a method for
reducing a bow wave.

[0025]FIG. 15 is an illustration of an alternate method of reducing a bow
wave.

[0026] FIG. 16 is an illustration of a flow diagram of aircraft production
and service methodology.

[0027] FIG. 17 is an illustration of a block diagram of an aircraft.

DETAILED DESCRIPTION

[0028] Referring first to FIGS. 1 and 2, a composite structure assembly 20
comprises a stiffener 21, sometimes also referred to as a first part, and
a spar 22 sometimes also referred to herein as a second part. The
stiffener 21 is bonded to a spar 22 by a layer of adhesive 40. The
stiffener 21 may comprise a fiber reinforced resin composite, and in the
illustrated example, has an I-shaped cross section formed by upper and
lower flanges 24, 26 joined together by a web 28. While an I-shape cross
section is shown in the Figures, the stiffener 21 may have other cross
sectional shapes, such without limitation, C, J, Z, L and inverted U
shapes. The spar 22 comprises a fiber reinforced resin laminate having a
web 30 and a flange 32 forming an L-shaped cross section, however other
cross section geometries are possible, such as, without limitation, a "C"
section. The spar 22 may form, for example and without limitation, part
of the airframe of an aerospace vehicle (not shown) such as a wing or a
stabilizer (not shown).

[0029] The web 30 transitions to the flange 32 through a radius 34 defined
between tangent points indicated by the broken lines 36 in FIG. 1. As
best seen in FIG. 2, the lower flange 26 of the stiffener 21 overlies and
is bonded to the upper surface 35 of the web 32. FIG. 1 illustrates a
mandrel 38 for supporting the spar 22 during consolidation and curing of
the spar 22. In the illustrated example, the stiffener 21 is a pre-cured
part that is bonded to the spar 22, however, in other embodiments, the
stiffener 21 may comprise an uncured composite part that is co-cured with
the spar 22. The shapes of the stiffener 21 and the spar 22 merely
illustrate a wide variety of possible part shapes and geometries.

[0030] Referring now to FIG. 3, after the stiffener 21 and the spar 22 are
assembled with a layer of adhesive 40 therebetween, a vacuum bag (not
shown in FIG. 3) is sealed over the assembly 20, which may then be placed
in an autoclave (not shown) for consolidation and curing. The radius 34
has an upper edge 45 that is spaced from the outer end 46 of the lower
flange of the stiffener 21. When evacuated, the bag may bridge over the
edge 45 of the radius 34. Bridging of the bag over the edge 45 may result
in a region 49 of low compaction pressure at the edge 45 when autoclave
pressure P is applied during consolidation and curing of the spar 22. The
applied compaction pressure P results in deformation of the fibers in the
upper plies 42 along the radius 34 which urges them to move in the
direction of the arrow 51 toward the region of low pressure 49. The
movement of the fiber toward to the low pressure region 49 may result in
the generation of a bow wave 44 in the upper plies 42 of the spar 22 as
the plies 42 are being compressed in the other areas of the radius 34.
This bow wave 44 may result wrinkles, voids or other undesired
inconsistencies in the spar 22 following curing.

[0031] Referring to FIG. 4, in order to reduce or eliminate the bow wave
44 shown in FIG. 3 caused by the region 49 (FIG. 3) of low pressure, a
device 48 is installed over the radius 34 of the spar 22 and the lower
flange 26 of the stiffener 21. The device 48 includes a first, bottom
caul 50 covering the radius 34 of the spar 22, including the upper edge
45. The upper extremity 56 of the first caul 50 abuts the outer end 26 of
the lower flange 26. The device 48 further includes a second, top caul 52
that rests on the lower flange 26 and overlies the upper extremity 56 of
the first caul 50. The second caul 52 overlaps the upper extremity 56 of
the first caul 50 by a preselected distance D. As will be discussed below
in more detail, in one embodiment, the first and second cauls 50, 52 may
be integrated into a single unit, while in other embodiments they may be
separate units. A vacuum bag 44 is sealed over the assembly 20 and is
used to apply compaction pressure to the parts and the caul 48.

[0032] As shown in FIG. 5, the first caul 50 includes an inside radius R
substantially conforming to the radius 34. The first caul 50 has a
thickness T at its upper extremity 56 which generally matches the
combined thickness of the lower flange 26 and the layer of adhesive 30.
The first caul 50 is tapered in its thickness from its upper extremity 56
to its lower extremity 58. The reduced thickness of the lower extremity
58 resulting from this tapering may reduce mark-off imparted to the spar
22 by the first caul 50 during the compaction process. In other
embodiments, the first caul 50 may not be tapered in its thickness.

[0033] Referring to FIG. 6, the second caul 52 includes a slotted web 52a
covering the web 28 of the stiffener 21, and longitudinally extending
flanges 52b which overlie the flanges 26 on the stiffener 21.

[0034] Referring to FIG. 4 in use, the device 48 is installed either as
two separate units or as a single unit on the assembly 20, such that the
first caul 50 overlies the radius 34 and has its upper extremity 56
abutting the outer end 26a of the flange 26. The slotted web 52a of the
second caul 52 is sleeved over the sides of the web 28 such that the
flanges 54 rest on the flanges 26 of the stiffener 21 and the outer end
60 overlies and rests on the upper extremity 56 of the first caul 50.
With the device 40 installed as described above, the vacuum bag 44 may be
installed over the assembly 20, and the assembly 20 may be processed in
an autoclave where pressure P is applied to the assembled parts. The
first caul 50 applies and distributes the autoclave pressure P to the
radius 34 including the upper extremity 56 which overlies the upper edge
45 of the radius 34. The autoclave pressure P also presses the flanges
52b against the flanges 26 of the stiffener 21 and against the upper
extremity 56 of the first caul 50.

[0035] Pressure applied to the lower flanges 26 is transferred by the
second caul 52 to the first caul 50. The tendency of the upper plies 42
(FIG. 3) to produce a bow wave 44 at the edge 45 is resisted by the
pressure applied to the upper extremity 56 by the forward end 60 of the
second caul 52. Thus, the upper plies 32 (FIG. 3) within the radius 34
are constrained to remain substantially in-plane during the compaction
process. Integrating the caul portions 50, 52 into a single part unit
provide the device 48 with additional stiffness 48 which may aid in
resisting generation of a bow wave 44 (FIG. 4) or similar heaving or
wrinkling of the outer plies 42 at the radius edge 45.

[0036] FIGS. 7 and 8 illustrate additional details of the second caul 52.
The upstanding web 52a includes a longitudinally extending slot 62
therein, and the flanges 52b extend laterally outward from the web 52a.
The forward end 60 extends beyond the web 52a and is adapted to overlie
the upper extremity 56 on the first caul 50, as shown in FIG. 4. The
second caul 52 may be fabricated from any suitable materials that possess
the requisite strength and stiffness, including but not limited to a
fiber reinforced resin composite such as, without limitation, carbon
fiber reinforced epoxy resin. During installation of the second caul 52,
the slot 62 receives the web 28 of the stiffener 21 is received within
the slot 62, and the flanges 52b rest on the flanges 26 of the stiffener
21.

[0037] FIG. 9 illustrates another embodiment of the device 48 in which the
first and second cauls 50, 52 are integrated into a single unit which may
be manufactured by molding the caul 48 around the end of the stiffener
21.

[0038] Attention is now directed to FIGS. 10, 11 and 12 which illustrate
another embodiment of the device 20 in which multiple devices 48 are
integrated into a unitized structure. In the illustrated example, two one
piece cauls 48 are arranged side by side and formed integral with a
connecting portion 66 and outer extensions 68. The first cauls 50 extend
substantially continuously across the entire length of the device 48. As
shown in FIG. 12, the device 48 may be installed as a single unit over
two adjacent stiffeners 21, covering the radius 34 on the spar 22 (not
shown in FIGS. 10-12). While the embodiment shown in FIGS. 10-12
integrates multiple devices 48 for use with multiple stiffeners 21 have
an I-shape cross section, the multiple integrated devices 48 may also be
adapted for use with stiffeners having other cross sectional shapes,
including, without limitation, C, J, Z, L and inverted U shapes.

[0039] Attention is now directed to FIG. 13 which illustrates another
method of compressing a radius 34 in a manner that reduces bow waves
generated during consolidation of the spar 30. In this example, the spar
30 is laid up over a mandrel 38 having a lateral extension 38a. The
lateral extension 38a includes a curved tool surface 70 that forms an
excess outwardly turned flange 72 having a large radius 74 which is
generally larger than radius 34. "Excess" refers to the fact that the
primary purpose of the flange 72 is to place the fibers in the radius 34
in tension, and that the flange 72 may not have other substantial
functional purpose. When consolidation pressure P is applied to the spar
30, pressure acting on the large radius flange 72 is greater than that
applied to the radius 34 and creates tension in the fibers in the upper
plies 42 (FIG. 3) which is transferred to the fibers in the radius 34.
This tension applied to the fibers in the upper plies 42 in the radius 34
may reduce or eliminate wrinkling and/or bow waves 44 in the area of the
radius 34, including the upper edge 45 (FIG. 3). As used herein, "large"
radius refers to a radius 74 that is large enough to produce the tension
in the upper plies 42 necessary to reduce or eliminate the bow waves 44.

[0040] Attention is now directed to FIG. 14 which illustrates a method of
joining composite parts in a manner that reduces bow waves in laminates
during curing. At step 76, first and second parts 21, 22 are assembled.
Next at step 78, a first portion 50 of a caul 48 is placed on the radius
34 of the first part 22 covering an edge 45 of the radius 34 and abutting
the first part 21. At step 80, a second portion 52 of the caul 48 is
installed on the second part 21, at least partially overlapping the first
caul 50 at the radius edge 45. In those embodiments where the caul
portions 50, 52 are integrated into a single unit, then steps 78 and 80
are combined into a single operation. At step 82, the assembled parts 21,
22 having the caul portions 50, 52 installed thereon are vacuum bagged.
At 84, a vacuum is drawn and consolidation pressure is applied to the
bag, using for example, autoclave processing. At step 86, caul portions
50, 52 are used to apply pressure to the radius 34 including the radius
edge 45 in order to transfer atmospheric pressure loads to the radius
edge 45 and reduce the formation of bow waves in the first part.

[0041]FIG. 15 illustrates the steps of a method of reducing bow waves in
a laminate using the apparatus shown in FIG. 14. At step 88, a large
radius 74 is formed in a laminate part 21 adjacent a smaller radius
section 34 in the part 21. At step 80, compaction pressure is applied to
the part 21, including applying tension on the fibers in the radius
section 34 by compressing the fibers in the large radius 74.

[0042] Referring next to FIGS. 16 and 17, embodiments of the disclosure
may be used in the context of an aircraft manufacturing and service
method 98 as shown in FIG. 16 and an aircraft 100 as shown in FIG. 17.
During pre-production, exemplary method 92 may include specification and
design 102 of the aircraft 100 and material procurement 104. During
production, component and subassembly manufacturing 106 and system
integration 108 of the aircraft 100 takes place. During step 106, the
disclosed method and apparatus may be employed to fabricate composite
parts such as fuselage sections which are then assembled at step 108.
Thereafter, the aircraft 100 may go through certification and delivery
110 in order to be placed in service 112. While in service by a customer,
the aircraft 100 may be scheduled for routine maintenance and service 114
(which may also include modification, reconfiguration, refurbishment, and
so on).

[0043] Each of the processes of method 98 may be performed or carried out
by a system integrator, a third party, and/or an operator (e.g., a
customer). For the purposes of this description, a system integrator may
include without limitation any number of aircraft manufacturers and
major-system subcontractors; a third party may include without limitation
any number of vendors, subcontractors, and suppliers; and an operator may
be an airline, leasing company, military entity, service organization,
and so on.

[0044] As shown in FIG. 17, the aircraft 100 produced by exemplary method
98 may include an airframe 116 with a plurality of systems 118 and an
interior 120. The disclosed method and apparatus may be employed to
fabricate fuselage sections which form part of the airframe 110. Examples
of high-level systems 118 include one or more of a propulsion system 122,
an electrical system 124, a hydraulic system 126 and an environmental
system 128. Any number of other systems may be included. Although an
aerospace example is shown, the principles of the invention may be
applied to other industries, such as the automotive industry.

[0045] The apparatus embodied herein may be employed during any one or
more of the stages of the production and service method 98. For example,
components or subassemblies corresponding to production process 106 may
be fabricated or manufactured in a manner similar to components or
subassemblies produced while the aircraft 100 is in service. Also, one or
more apparatus embodiments may be utilized during the production stages
106 and 108, for example, by substantially expediting assembly of or
reducing the cost of an aircraft 100. Similarly, one or more apparatus
embodiments may be utilized while the aircraft 100 is in service, for
example and without limitation, to maintenance and service 114.

[0046] Although the embodiments of this disclosure have been described
with respect to certain exemplary embodiments, it is to be understood
that the specific embodiments are for purposes of illustration and not
limitation, as other variations will occur to those of skill in the art.

Patent applications by Thomas J. Kennedy, Bonney Lake, WA US

Patent applications in class Direct application of vacuum or fluid pressure during bonding

Patent applications in all subclasses Direct application of vacuum or fluid pressure during bonding